The present invention relates to a method of manufacturing a part made of composite material as well as a tool for the implementation thereof. The invention more particularly relates to a method of manufacturing an aircraft fuselage frame.
According to an embodiment shown in FIG. 1, a fuselage frame 10 is in the form of a profile having a Z-shaped cross-section whose central portion referred to as a core 12 forms a complete or partial ring. The profile comprises a first wing 14 referred to as an inner wing arranged in the area of the inner edge of the core 12 and perpendicular to the latter and a second wing 16 referred to as an outer wing arranged in the area of the outer edge of the core 12, also perpendicular to the latter.
A method of manufacturing such frame from composite material is described in document FR 2.928.295.
According to this document, first, a substantially rectangular strip is made from a stack of three pre-impregnated fiber plies, each ply having fibers oriented along a direction, the strip comprising plies with different orientations of fibers, a ply with fibers at 30°, a ply with fibers at 90°, and another ply with fibers at 150°.
Second, the strip of fiber plies is arranged on a mandrel made of deformable material then compressed on this mandrel so as to conform to the shape thereof.
The deformable mandrel is capable of becoming deformed between a rectilinear position and a curved position but has an incompressible or quasi-incompressible transverse section.
Then, the deformed strip arranged on the mandrel made of deformable material is placed in contact with a heated tool having, at its periphery, radial sections with a profile, complementary to the transverse sections of the mandrel. Thus, during bending, the strip is compressed and subjected to a rise in temperature.
Subsequent to the setting in place of this first strip, a second strip having three plies of pre-impregnated fibers is cut out to be arranged on another deformable mandrel and then compressed on the latter.
Then, this second strip, deformed on its mandrel made of deformable material, is placed in contact with the first strip still in place on the tool then compressed against the first strip.
To obtain a frame, it is necessary to attach, as mentioned previously, several strips on top of one another, before polymerizing the assembly thus formed.
More conventionally, according to a mode of operation, to make a part from composite material, first a preform 18 of pre-impregnated fibers is made by stacking layers 20 on top of one another on a laying surface 22 of a tool 24, as shown in FIG. 2, then this preform 18 is subjected to a polymerization phase.
The present invention relates more particularly to this polymerization phase during which the preform 18 is covered with a lining 26.
On a functional level, this lining 26 must:
provide a geometrical shape to one of the surfaces of the preform;
ensure the compression of the preform from an outer pressure;
allow gas included in the preform to be extracted; and
allow the preform to be heated while minimizing thermal gradients.
According to an embodiment, the tool 24 comprises a gas extraction apparatus which opens out, via at least one opening 28, in the area of the laying surface 22, outside the zone covered by the preform, yet at a reduced distance from said zone.
The lining 26 comprises:
a conforming plate 30 whose peripheral edges 32 are slightly set back relative to the peripheral edges (or flanks) 34 of the preform;
draining fabrics 36 provided at the periphery of the preform 18 and conforming plate 30 in contact with the laying surface 22 in the area of the openings 28 of the gas extraction apparatus;
an unmolding film 38 covering the conforming plate 30;
a drainage felt 40 which covers the conforming plate 30 and the draining fabrics 36; and
a bladder 42 which is connected to the laying surface 22 via sealing means 44 in the periphery of the draining fabrics 36.
After the lining has been set in place, the preform is subjected to a polymerization phase after which the fibers are embedded in a resin matrix, which is accompanied with a contraction of the preform causing a thickness reduction on the order to 5 to 12%.
The lining 26 of the prior art is not entirely satisfactory for the following reasons:
Setting in place different layers of lining is lengthy and tedious, even more so if the surface to be covered is non-developable.
Considering the complexity thereof, the setting in place of the lining can only be done manually and cannot be automated.
The different lining elements are costly at the time they are purchased as well as recycled at the end of their lifespans.
When the surface of the part in contact with the lining is non-developable, the risks of rupture of the bladder are not negligible during polymerization, which causes the part to be rejected.
Finally, this type of lining does not guarantee control over the geometry of the surface covered by the lining for the following reasons:
First, the outer pressure applied to one of the surfaces of the conforming plate is not strictly all around equal to the reaction force exerted by the preform on the opposite surface of the preform. Because the conforming plate is in contact only with the preform, it is not stabilized and can move slightly due to this difference of forces, which means that geometric tolerances (more particularly those pertaining to thicknesses) may not be respected.
Second, when the outer surface of the conforming plate is non-developable, the bladder exerts forces on the conforming plate which may be not strictly oriented according to the norm and cause the deformation or displacement of said conforming plate, which means that geometric tolerances (more particularly those pertaining to thicknesses) may not be respected.